Karl Popper did some interviews with an Italian journalist in 1991. They appeared in a book The Lesson of This Century.
He regarded himself as an optimist because he was convinced that the western democracies achieved a level of broad-based prosperity and freedom that was unprecedented, despite the desperate and even hysterical condemnation of democratic capitalism by the usual suspects.
However he attached a caveat to him optimism.
OPTIMISM AND THE DANGER OF THE MEDIA
Fortunately the truth is easy to verify: the truth that we in the West live in the best world that has ever existed. We cannot allow this truth to go unsaid. The media, which are the most guilty in this respect, need to be convinced that they are causing great harm. They must be persuaded to do their bit. The media must be persuaded to see and tell the truth, to realize the hidden danger that they themselves represent, to develop a self-critical attitude (as any healthy institution does), and to correct themselves. This is a new task for them. But they are doing great harm. And unless they cooperate, it will be almost impossible to remain an optimist.